>"why aren't they hating each other?"

French and German relations are way more interesting and surprising from this point of view. From Napoleon (who humiliated Prussia) to 1870 to WW1 and WW2... France and Germany went from extremely bitter rivals, for generations (way more than the UK and US ever was let's be honest) to close allies in a few decades after WW2.

Hell, Franco-English relations are also surprising in a similar way (although it took more time).